Plastering and painting advice needed

[pineapple]

Renovating an old limestone cottage. The outside has been covered with something or other and painted so probably not breathable (I know I know). There was a major damp issue on the first floor gable end internal wall - in line with the chimney flue. We hacked off all the plaster to that wall and carried out chimney repairs ncluding fitting flashing :!: That seems to have stopped further water ingress and it is drying out. At the moment the stonework is damp down the first 3 or 3 foot from the ceiling and 1-2 foot across.
The chimney/stove guy has recommended that the wall is left as long as possible (whatever that means) then plastered with lyme plaster followed by renovating plaster. However the builder doing most of the work is adamant that we can dry line the wall and moisture will still be able to escape and I will have a useable room in the meantime. I don't want to make a problem worse but on the other hand don't want to live with a building site forever. Advice please!
The second issue is that before I had even heard of lyme plaster, another bedroom was completely replastered in standard plaster.
Just wondering if I should go for a breathable paint such as a clay based one or whether it is a pointless exercise over ordinary plaster.
Cheers

 

[kreyszig]

I would have thought it fine to use lime plaster on damp walls - you normally need to wet the brick/stone before applying to make sure it doesn't suck all the moisture out of the mixture, which is necessary for a chemical set (hydraulic lime - hydrated is different).
I guess you might want to wait before painting though.

Not sure about putting "renovating plaster" over the top, that sounds dodgy to me.

Dry lining doesn't really go too well with old properties in my opinion, and quite likely a few others on here will agree. If you were to do it, I think you'd be better off with a stud framework, rather than using "dot and dab" - which is a recipe for damp plasterboard. But I reckon the best approach is likely to be lime plaster and leave it at that until it's paintable.

 

[malcolm]

For plastering directly on a wall - lime will allow the wall to breathe and continue to dry. It is no more difficult to use than any other type of plaster.

Normal plaster (gypsom) doesn't like to get wet so will tend to go a bit mouldy and fall off if the wall has no other way to breathe.

Renovation plaster gets around this by being made of cement or a cement lime mix which is more waterproof. It will keep the inside of the room dry but the wall behind will be sodden wet and crumble.

Is the outside of the wall cannot breathe I would consider a stud wall with an air gap of at least an inch to the wall. Make sure the air gap is vented to the roof space. It is not an ideal solution as you won't be able to see when the wall is getting wet which would be a problem if there are any timbers embedded in the wall. Nicer (but very much more expensive) to allow the outside of the wall to breathe.

 

[pineapple]

Cheers
Well we think we have sorted out the cause of the damp so there shouldn't be any extra.
Fingers crossed.

 

[plasticpigeon]

I'm not a fan of dot and dab, but I'd have thought that upstairs, so long as no more water is coming in, modern plaster should be ok. Gypsum does crumble away eventually if it gets damp so it is not good for an area that is still damp and drying. As others have said, dry lining a damp and drying area when still damp doesn't sound very sensible unless the moisture can actually vent to somewhere and isn't confined to the space behind the plasterboard.

 

[MatthewC]

For plastering directly on a wall - lime will allow the wall to breathe and continue to dry. It is no more difficult to use than any other type of plaster.

I reckon, for an amateur, that lime plaster is easier as it stays workable for longer!

Normal plaster (gypsom) doesn't like to get wet so will tend to go a bit mouldy and fall off if the wall has no other way to breathe.

Renovation plaster gets around this by being made of cement or a cement lime mix which is more waterproof. It will keep the inside of the room dry but the wall behind will be sodden wet and crumble.

As has been said before, if you use anything containing cement on your period property, you compromise the integrity of the building because it is often irreversible - completely removing it when dampness gets in (as it does so often, through whatever means, some time in the distant future) is either impossible or may cause great damage.

Matthew